1. Field of the Invention
The subject invention relates to tunable semiconductor oscillators.
2. Description of Prior Art
Prior art considered to be relevant herein is disclosed in U.S. Pat. No. 4,009,454, issued on Feb. 22, 1977, on an invention by J. Darrow and in U.S. Pat. No. 3,407,363, issued on Oct. 22, 1968, on an invention by N. Kaiser et al.
U.S. Pat. No. 4,009,454 discloses a constant amplitude signal generating circuit, the circuit comprising a shunt type voltage regulator providing a constant voltage source to a free-running transistor oscillator. The regulator includes first and second series connected resistors in series with a B+ supply and a zener diode, the anode of the diode being connected to a grounded terminal of the supply. A junction common to the first and second resistors is coupled to ground by third and fourth series connected resistors and a junction common to the third and fourth resistors is coupled via a feedback winding of a transformer to the base of a transistor of the oscillator. The collector of the transistor is connected by the primary winding of the transformer to the second resistor and the cathode of the zener diode and is coupled by a capacitor to ground. In addition, the emitter of the transistor is coupled by a feedback resistor to ground. Inductance provided by the transformer and the capacitor determine the frequency of oscillation of the circuit. The values of the second, third, and fourth resistor are chosen such that the DC operating point of the transistor is on the linear portion of the dynamic transfer characteristic curve. In operation, the transistor is alternately driven between saturation and cutoff. Therefore, a slight clipping effect is associated with the signal generated. An output signal, similar to the generated signal, is provided by a secondary coil of the transformer.
U.S. Pat. No. 3,407,363 discloses a varactor tuned oscillator. The oscillator comprises a transistor whose base is coupled to its collector by a turned circuit which includes an inductor connected in parallel with a pair of series connected varactors. A DC source coupled to the emitter of the transistor and a center tap on the inductor supplies power to the oscillator. The oscillator is said to operate in class C.